In several prior fuel injection systems having a pump which supplies fuel to a fuel injector, the pump supplies more fuel than is required by the injector, and the excess fuel is discharged through a fuel pressure regulator represented, for example, by U.S. Pat. No. 3,511,270. The fuel pressure regulator has a diaphragm which balances the pressure of the fuel supplied to the injector with the bias of a pressure regulator spring. If the pressure of the fuel supplied to the injector is less than the spring bias, the diaphragm positions a valve to shut off the excess fuel flow and thus increase the fuel pressure at the injector; if the pressure of the fuel supplied to the injector exceeds the spring bias, the diaphragm retracts the valve to discharge the excess fuel and thus reduce the fuel pressure at the injector.
It is evident, therefore, that the fuel pressure at the injector is determined by the bias of the pressure regulator spring, and the desired fuel pressure is established by adjusting the bias of the spring. Prior fuel pressure regulators included an adjusting screw which adjusted the spring bias by moving a seat that engages the end of the spring.